Friction compensator

ABSTRACT

A pressure vessel having an actuating system for advancing and retracting an element, e.g. a piston, slidably into and out of the vessel is provided with means responsive to frictional forces generated by the sliding passage of the element into and out of the vessel to generate a compensating force for opposing the effect of the frictional force on the actuating system.

United States Patent John Edward Beroset Alsace Township, Berks Co.,Pa.; Francis Joseph Fuchs, Jrt, Princeton Inventors Junction, NJ. Appl.No. 812,205 Filed Apr. 1, 1969 Patented Mar. 23, 1971 Assignee WesternElectric Company-Incorporated New York, N.Y.

FRICTION COMPENSATOR 7 Claims, 3 Drawing Figs.

US. Cl 60/54.6, 92/ l 71 Int. Cl FlSb 7/00 Field ofSearch... 60/54, 516

[56] References Cited UNITED STATES PATENTS 2,032, I 85 2/1936 Sciaky60/54.5HA 2,058,377 10/1936 Francis..... 60/54.5HAX 2,351,872 6/ 1 944Parker 60/54.5HA 2,608,059 8/1952 Kux 60/54.5HA 2,656,745 10/1953Forichon 60/54.5HAX 2,774,217 12/ 1 956 Ashton 60/54.5HA 2,827,7663/1958 Hufford 60/54.5HA

Primary Examiner-Martin P. Schwadron Assistant ExaminerA.M. ZupcicAttorneys-H. J. Winegar, R. P. Miller and W. M. Kain ABSTRACT: Apressure vessel having an actuating system for advancing and retractingan element, e.g. a piston, slidably into and out of the vessel isprovided with means responsive to frictional forces generated by thesliding passage of the element into and out of the vessel to generate acompensating force for opposing the effect of the frictional force onthe actuating system.

I FRICTION COMPENSATOR BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to pressure vessels having elementsslidably movable into and out of the vessels, and specifically tofriction compensators for such vessels. More particularly, thisinvention is related to an improvement in fluid systems, for example,fluid systems which are utilized to operate high-pressure fluid vesselsof the type having an inner working fluid chamber and one or more outersupport fluid chambers. Vessels of this type may be utilized, forcontaining ultrahigh fluid pressures, for example, in fluid pressureintensifiers (apparatus for increasing the pressure of and for pumpingfluid), in fluid pressure amplifiers (apparatus for increasing thepressure of a fluid), and in apparatus wherein an ultrahigh-pressureenvironment is required for accomplishing some function such as testingor high-pressure metal forming.

2. Description of the Prior Art Considering briefly the nature anddevelopment of the type of pressure vessels which may be served by thepresent invention,,it is known by those having skill in this art thatearly approaches to the development of vessels capable of withstandingultrahigh pressures proceeded along the lines of increasing the size andtherewith the load-carrying capacity of known pressure vessel designs.Such approaches fell short of the art requirements, however, in thatthey were limited by the strength of materials available for use, by theunwieldy sizes of vessels of known configuration, which sizes wererequired by the ultrahigh stresses, and by the relatively high expenseinvolved in providing complex stress-relieving structural arrangements.

More recent pressure vessels, which have been capable of supportingultrahigh pressures. have utilized a body of pressurized fluidsurrounding and acting upon an inner cylinder to support or assist theinner cylinder in supporting a body of pressurized working fluid. Insuch vessels, support fluid for acting upon the inner cylinder to assistin supporting the pressure of the working fluid ordinarily has beenpressurized by a pressure amplifier mounted externally of the vessel.The working fluid, however, ordinarily has been pressurized by areciprocable piston or plunger extending directly into the working fluidchamber defined by the inner cylinder.

Generally, both the support fluid pressure amplifier and thereciprocable piston for pressurizing the working fluid have been poweredby a common actuating fluid system so that a predetermined relationshipbetween the pressure in the working fluid and the pressure in thesupport fluid is established and maintained at all times. In otherwords, by utilizing a common body of fluid to actuate the pressurizingapparatus for both the support fluid and the working fluid, it istheoretically insured that increases or decreases in the pressure of theworking fluid are accompanied by proportional increases or decreases inthe pressure of the support fluid so that at any time in the operatingcycle of the apparatus, the pressure of the support fluid is neitherinsufficient nor too great for assisting the inner cylinder insupporting'the working fluid pressure.

Obviously, neither excessive nor insufficient support fluid pressure isdesirable, since support fluid pressures which are either greater orless than those required to assist the inner cylinder in supporting theworking fluid pressure may cause undesirable deformation of the innercylinder, work hardening of the inner cylinder material and, ultimately,catastrophic failure of the inner cylinder by implosion if the supportfluid pressure is excessive, or by explosion if the support fluidpressure is insufficient. It can be seen, therefore, that propercoordination of support fluid pressure and working fluid pressure is aprimary consideration in operating ultrahigh pressure vessels of thetype utilizing support fluid.

' In this regard a problem which has been experienced in those apparatuswherein the working fluid is pressurized by a reciprocable piston orplunger extending into the working fluid chamber defined by the innercylinder and where both the reciprocable piston and the apparatus forgenerating pressure in the support fluid are actuated by a commonactuating fluid system, is that the pressure in the actuating fluidsystem has not, at all times during the operation of the apparatus,accurately reflected the pressure of the working fluid.

The source of the inaccuracy in the relationship between the pressure inthe actuating fluid system and pressure in the working fluid has beenfound to be the frictional force generated by the sliding engagementbetween the reciprocable piston or plunger and seal structure whichprecludes leakage of fluid from the working fluid chamber. Suchfrictional force has been found either to add to, during pistonadvancement, and subtract from, during piston retraction, the force onthe piston or plunger generated by the pressure of the working fluidacting thereon. The resultant force is supported by the pressure of thefluid in the actuating fluid system. Thus, where such frictional forcesoccur, the pressure in the actuating fluid system is not a directindication of the true pressure within the working fluid chamber.Rather, the pressure in the actuating fluid system reflects both theeffect of the pressure within the working fluid chamber and thefrictional force generated by reciprocating movement of the piston.

vThe difficulties presented by the effect of frictional forces areclear. For example, if the pressure in the actuating fluid system issuch as to indicate a particular pressure in the working fluid when, inactuality, the pressure of the working fluid when, in actuality, thepressure of the working fluid is more or less than the indicatedpressure, the pressure generated in the SUMMARY OF THE INVENTION.

The present invention overcomes the above-discussed problems byproviding, in a pressure vessel having an actuating system for advancingand retracting an element slidably into and out of the vessel, a meansresponsive to frictional forces generated by the sliding passage of theelement into and out of the vessel to generate a compensating force foropposing the effect of the frictional force on the actuating system. Forexample, the present invention may embody a seal friction compensatorfor use with a fluid-actuated, fluid-supported high-pressure vesselhaving a piston means slidably extending into the vessel through asealed bore, the compensator comprising means responsive to thefrictional forces generated by the sliding passage of the piston meansthrough the sealed bore to generate a compensating force, substantiallyequal in magnitude and opposite in direction to the frictional force,for compensating for the effect of the frictional force on the fluidactuating system of the high pressure vessel.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of thepresent invention may be had from a consideration of the followingdetailed description thereof when read in the light of the accompanyingdrawings, wherein:

FIG. 1 is a cross-sectional elevational view of a high-pres sure vesselprovided with a seal-friction compensator apparatus in accordance withthe present invention;

FIG. 2 is a schematic diagram of the vessel of FIG. I, showing theforces exerted on the various apparatus elements during the operation ofthe apparatus of FIG. I; and

FIG. 3 is a schematic diagram of a pressure vessel provided with anotherembodiment of seal-friction compensator in accordance with the presentinvention.

DETAILED DESCRIPTION Considering the present invention in detail andreferring in particular to FIG. 1, a high-pressure vessel, in use as afluidpressure intensifier and designated generally by the referencenumeral 10, is provided with a seal friction compensator designatedgenerally by the reference numeral 12.

As discussed above, high-pressure vessels of the type underconsideration may be utilized inter alia as fluid-pressure intensifiers,fluid-pressure amplifiers and as apparatus for establishing andmaintaining a high-pressure environment in which to conduct a functionsuch as testing or high-pressure metal forming. In this regard, it is tobe recognized that although vessel is disclosed in use as afluid-pressure intensifier, the discussion with respect thereto isequally appropriate for like pressure vessels in other uses, e.g. asfluid-pressure amplifiers or other apparatus.

Pressure vessel 10 comprises an outer main support member, such as outer14, a central support member, such as inner cylinder 16, which ispositioned concentrically within but s aced from outer cylinder 14, andtop and bottom end plugs 18 and 19 respectively. End plugs 18 and 19 aregenerally cylindrical and have outer circumferential surfaces 20, 21 andthreaded portions 22 and 23 respectively, the basic diameters of whichthreaded portions are smaller than the basic diameters of outer surfaces20, 21 and substantially equal to the diameters of annular channels 25and 26 provided at the upper and lower ends of the inner surface ofcylinder 14 as seen in FIG. 1. Channels 25, 26 are threaded forreceiving the threaded portions 22, 23 of end plugs 18, 19 respectively,and are provided with shoulders 30, 31 at their inner ends foraccommodating high-pressure seals 35 and 36 respectively. Radiallyextending shoulder surfaces 38, 39 are provided on plugs 18, 19 betweenouter surfaces 20, 21 and threaded portions 22, 23. These shoulderscooperate with the upper and lower surfaces 40, 41 of outer cylinder 14to limit the insertion of plugs 18 and 19 into the cylinder and toprovide a snug, surface-to-surface engagement between the end plugs 18,19 and the outer cylinder 14.

lnner cylinder 16 extends from the bottom surface of top plug 18 to thetop surface of bottom plug 19 and cooperates with the top and bottomplugs to define a first or working fluid chamber 42 for containing aworking fluid. Additionally, inner cylinder 16 cooperates with top andbottom end plugs l8, l9, and outer cylinder 14, to define a second orsupport fluid chamber 44 for containing a support fluid. Ring seals 35,36, which may be of any of the high-pressure types known in the art,e.g., the generally U-shaped Teflon cup seal with antiextrusion rings asshown, are provided at the upper and lower surface of support fluidchamber 44. Upper seal 35 is received within an annular groove definedby the cooperation of channel 25 and shoulder of outer cylinder 14 withthe lower surface of end plug 18, and lower seal 36 is received withinan annular groove defined by the cooperation of channel 26 and shoulder31 of outer cylinder 14 with the upper surface of bottom end plug 19.Seals and 36 are sized so as to tightly engage the outer surface ofinner cylinder 16, the surface of channels 25, 26 respectively, and therespective inner surfaces of end plugs 18, 19 to preclude the leakage ofsupport fluid out of second or support fluid chamber 44.

Top and bottom plugs 18, 19 are provided with centrally disposed,longitudinally axially extending through bores 50, 51 respectively.Slidably received in through bore 50 in top plug 18 is a reciprocablemain piston 54. In a similar manner, there is slidably received inthrough bore 51 in bottom plug 19 a discharge pipe 56 for dischargingworking fluid from working fluid chamber 42. Main piston 54 and pipe 56are of equal diameters and are sized so as to at all times extendpartially into working fluid chamber 42. Thus, the outer surface of mainpiston 54 cooperates with the inner surface of inner cylinder 16 and thebottom surface of top plug 18 to define an annular channel for receivingan upper ring seal 60. Similarly, the outer surface of pipe 56cooperates with the inner surface of inner cylinder 16 and the topsurface of bottom plug 19 to define an annular channel for receiving alower ring seal 61. Ring seals 60, 61 which may be of the same type asseals 35, 36, i.e. the generally U-shaped Teflon cup seal withantiextrusion rings as shown, prevent the leakage of working fluid fromworking fluid chamber 42 either past main piston 54 and pipe 56, or pastinner cylinder 16 into support fluid chamber 44.

lnner cylinder 16 is provided with an integrally formed dependent pipeportion 62 having a passage 63 therein, which passage extends upwardlywith inner cylinder 16 and thereafter, from a point radially adjacentsupport fluid chamber 44, radially outwardly through the outer surfaceof the inner cylinder. Passage 63 accommodates the introduction ofsupport fluid pressure from a pressure amplifier which is designatedgenerally by the reference numeral 64, to support fluid chamber 44.The'lower end of pipe 62 extends through a bore 65 formed in bottom plug19, whereafter pipe 62 is operably connected to a fluid line 68 leadingto the high-pressure discharge side of pressure intensifier 64.

The positioning of passage 63 within pipe portion 62 and inner cylinder16 provides the pressure vessel 10 with a lower incidence of stressconcentrations thereby allowing the overall size of the vessel structureto be minimized. In this regard, a complete disclosure of such pressurevessel structure is contained in the copending application of J W.Archer et al., Ser. No. 652,112 now US. Pat. No. 3,490,344 which wasfiled on Jul. 10, 1967 and assigned to the same assignee as the presentinvention.

Main piston 54 extends upwardly from working fluid chamber 42through'zbore 50 in top plug 18 and thereafter through a main fluidmotor 70 mounted externally of pressure vessel 10. Main fluid motor 70comprises an outer cylindrical wall 72 which is closed at its upper andlower ends by transverse walls 73, 74, respectively, to define a chambertherein. Centrally disposed, longitudinally axially extending bores 76,77 are provided in transverse walls 73 and 74, respectively, toaccommodate the sliding extension of piston 54 therethrough. Formed onpiston 54 within the chamber of main fluid motor 70 is an actuatorpiston 79. Actuator piston 79 is of a diameter which is substantiallyequal to the inside diameter of cylindrical wall 72 and cooperatestherewith to define an advance fluid chamber 81 thereabove. and aretraction fluid chamber 82 therebelow. An O-ring seal 84, mounted in asuitable channel on the peripheral surface of actuator piston 79,establishes a fluid-tight seal between actuator piston 79 and the innersurface of outer cylindrical wall 72 so as to prevent fluidcommunication between advance fluid chamber 81 and retraction fluidchamber 82. Similarly, suitable seals 86, 87, eg O-ring seals. areprovided in annular channels formed in bores 76, 77, respectively, topreclude leakage of fluid from advance fluid chamber 81 and retractionfluid chamber 12 around the surface of piston 54.

Formed in the upper transverse wall 73 of main fluid motor 70 is apassage 89 which communicates advance fluid chamber 81 with an advancefluid line 90 which is connected to fluid line 94 leading from a sourceof advance fluid (not shown). Similarly, formed in lower transverse wall74 of main fluid motor 70 is a passage 92 which communicates retractionfluid chamber 82 with a retraction fluid line 93 which is connected to afluid line 98 leading from a source or retraction fluid (not shown).

Formed centrally of piston 54 is a longitudinally axially extending bore95 which communicates working fluid chamber 42 with a source of workingfluid (not shown). The flow of working fluid through bore 95 isrestricted to flow only into working fluid chamber 42 by a check valve96 mounted in the upper end of bore 95. Thus, during the operation ofpressure vessel 10 as a pump or intensifier as discussed below, chamber42 is charged with fluid through valve 96 and bore 95 in piston 54, andthereafter the fluid is discharged through pipe 56 which is alsoprovided with a check valve 97 to allow the flow of fluid out of chamber42 through pipe 56 while precluding the entry of fluid from pipe 56 toworking fluid chamber 42.

As is shown in FIG. 1, pressure vessel 10 is enclosed and looselysupported by a mounting cylinder, designated generally by referencenumeral 99 which is securely mounted on a rigid support 11. Mountingcylinder 99 comprises an upper cylindrical section 101 which is inthreaded engagement with a lower cylindrical section 102. Formed on theupper end of upper cylindrical section 101 is a radially inwardlyextendtherewith.

The lower surface of upper flange 104, the circumferential surface 20 of'top plug 18, the inside surface of mounting cylinder 99 and the uppersurface 40 of outer cylinder 14 cooperate to define a first annularfluid chamber 110. Similarly, the upper surface of lower flange 106, thecircumferential surface 21 of bottom plug 19, the inside surface ofmounting cylinder 99 and the bottom surface 41 of outer cylinder 14cooperate to define a second annular fluid chamber 112.

First fluid chamber 110 is sealed against leakage around top plug 18 bya seal 114 mounted in an annular channel formed in the innercircumferential surface 108 of upper flange 104, and is also sealedagainst leakage around outer cylinder 14 by a seal 115 mounted in anannular channel formed in the inner surface of upper cylindrical section101. Second annular fluid chamber 112 is sealed against leakagetherefrom around bottom plug 19 by a seal 117 mounted in an annularchannel fonned in the inner circumferential surface 109 of lower flange106, and also is sealed against leakage around outer cylinder 14 by aseal 118 mounted in an annular channel formed in the inner surface oflower cylindrical section 102.

First annular fluid chamber 110 is in communication with pressureamplifier 64 through a passage 122 in upper flange 104 and a fluid line123 extending from passage 122 to amplifier 64. Second annular fluidchamber 112 is also in communication with pressure amplifier 64 througha passage 125 in lower flange 106 and a fluid line 126 extending frompassage 125 to amplifier 64. As is discussed below, pressure vessel ismovable within mounting cylinder 99 to pressurize the fluid withinchambers 110 and 112 in response to the frictional forces between piston54 and seal 60. Vessel 10 and cylinder 99 define a sensing fluid motor,designated generally by the reference numeral 128, for sensing thefrictional forces generated between the piston 54 and seal 60 and fortransmitting a pressure signal indicative of the sensed forces to acompensator fluid motor, designated generally by the reference numeral130, which is formed as a part of fluid pressure amplifier 64 and whichis provided to exert a controlling force in fluid pressure amplifier 64.

Fluid pressure amplifier 64 is a dual motor amplifier comprising asupport fluid motor designated generally by the reference numeral 129,in tandem with compensator fluid motor 130. More specifically, fluidpressure amplifier 64 comprises a generally cylindrical casing 133 beingclosed at one end by a first sealed threaded end plug 134 and at theother end by a second sealed threaded end plug 135.

Second threaded end plug 135 is a longitudinally axially deep plughaving a bore 136 extending longitudinally axially from the upper endfor substantially the entire depth thereof. The lower end of end plug135 is in communication with bore 136 through a passage 137 whichaccommodates the connection of fluid line 68 from support fluid chamber44.

Disposed substantially centrally of casing 133 is a transverselyextending partition 140 which serves to divide the internal volume ofcasing 133 into an upper chamber 142 and a lower chamber 143.Transversely extending partition 140 is provided with a centrallydisposed, longitudinally axially extending through bore 145 whichcommunicates upper chamber 142 with lower chamber 143. Slidably receivedthrough bore 145 is a piston rod 147 which extends from bore 136 formedin end plug 135, through lower chamber 143 and bore 145 into upperchamber 142. That portion of piston rod 147 which extends into bore 136defines an intensifier piston for pressurizing the fluid in supportfluid chamber 44 through passage 63 and fluid line 68. Mounted in (orformed integrally with) piston rod 147 are a support piston 148 and acompensator piston 1497 Support fluid piston 148 on piston rod 147 ispositioned within lower chamber 143 and is'of a diameter substantiallyequal to the inside diameter of cylindrical casing 133 so as to dividelower chamber 143 into an upper or advance fluid section 151 and a loweror retraction fluid section 152. The peripheral surface of support fluidpiston 148 is provided with a ring seal 154 so as to prevent thecommunication of fluid around piston 148 between advance fluid section151 and retraction fluid section 152. Compensator piston 149 on pistonrod 147 is positioned within upper chamber 142 and is of a diametersubstantially equal to the inside diameter of cylindrical casing 133 soas to divide upper chamber 142 into an upper or booster fluid section156 and a lower or retarding fluid section 157. The peripheral surfaceof compensator piston 149 is provided with a ring seal 159 so as toprevent the communication of fluid around piston 149 between boosterfluid section 156 and retarding fluid section section 157. Thecommunication of fluid between retarding fluid section 157 and advancefluid section 151 around piston rod 147 is prevented by a ring seal 161mounted in an annular channel formed in the surface of bore 145.

Formed in generally cylindrical casing 133 are four radially extendingfluid passages 163, 164, 165 and 166. Fluid passage 163 accommodates thecommunication of booster fluid section 156 with fluid line 123 andtherethrough to first annular fluid chamber 110. Fluid passage 164accommodates the communication of retarding fluid section 157 with fluidline 126 and therethrough ultimately to second annular fluid chamber112. Fluid passage 165 accommodates the communication of advance fluidsection 151 with fluid line and therethrough ultimately to advance fluidchamber 81 of main fluid motor 70. Finally, fluid passage 166accommodates the communication of retraction fluid section 152 withfluid line 93 and therethrough ultimately to retraction fluid chamber 82of main fluid motor 70.

The operation of fluid pressure intensifier 10 can best be describedwith reference to FIG. 2 which is a schematic diagram of the vessel ofFIG. 1. With regard to FIG. 2, sensing fluid motor 128 is shown, forpurposes of description as a fluid motor independent of the structure ofpressure vessel 10 rather than as a concentric fluid motor havingpressure vessel 10 for a piston as is actually shown in FIG. 1.Additionally, support fluid motor 129 and compensator fluid motor 130,which are shown in FIG. 1 as being integral to define fluid pressureamplifier 64, are shown in FIG. 2 as being separate fluid motorsconnected by a common piston rod. Finally, bore and check valve 96through which working fluid is introduced to working fluid chamber 42and which are shown in piston 54, are shown in FIG. 2 for descriptivepurposes as being independent structure. In all other respects, however,the schematic presentation of FIG. 2 corresponds to the structure ofFIG. 1.

In the operation of fluid pressure intensifier 10, and referringprimarily to FIG. 2, working fluid chamber 42 is filled with fluid, thesupport fluid system (including chamber 44, passage 63, fluid line 68and bore 136 of fluid pressure amplifier 64) is filled with fluid, thecompensator fluid system (including annular fluid chambers 110, 112,booster fluid section 156, retarding fluid section 157 and theirconnecting passages and fluid lines) is filled with fluid, advance fluidis introduced to advance fluid chamber 81 of main fluid motor 70 and toadvance fluid section 151 of support fluid motor 129 through fluid line90, and retraction fluid is introduced to retraction fluid chamber 82 ofmain fluid motor 70 and retraction fluid section 152 of support fluidmotor 129 through retraction fluid line 93.

Additional pressurized advance fluid is then introduced to advance fluidchamber 81 and advance fluid section 151 through fluid line 90. Thispressurized advance fluid bears upon actuator piston 79 to generate adownwardly directed force F,,. thcrcagainst. Force F, tends to displaceactuator piston 79 downwardly. thus causing main piston 54 to increasethe pressure in the working fluid chamber 42. Thereafter, the continuedexertion of force F,,. displaces main piston 54 into chamber 42 todischarge the working fluid through discharge line 56.

Concurrently with the increase of the pressure of the working fluid inchamber 42, the pressure of the support fluid in chamber 44 is alsoincreased by the action of advance fluid in advance fluid section 151exerting pressure on support fluid piston 148 to generate a downwardlydirected force F thereagainst. Force F, tends to displace piston rod 147downwardly within bore 136 so as to increase the pressure of the fluidtherein, which pressure increase is transmitted to support fluid chamber44 through fluid line 68 and passage 63 so as to generate support fluidpressure in chamber 44 to assist inner cylinder 16 in supporting theultrahigh fluid pressures within working chamber 42. In this regard andas mentioned above, in order for the support fluid in chamber 44properly to assist inner cylinder 16 in supporting the load exertedthereon by the pressure of the working fluid in chamber 42, the supportfluid pressure should be maintained at a predetermined ratio withrespect to the pressure of the working fluid. To this end, the areas ofpiston 79 and 148 are sized so as to generate forces F,,] and F. actingthrough main piston 54 and piston rod 147 respectively, generatepressures in the working fluid and support fluid which are at thepredetermined ratio desired to accomplish proper operation of theapparatus; i.e., the pressurized support fluid in chamber 44 actingradially inwardly against the outer surface of cylinder 16 generates aradially inwardly acting force substantially equal to the radiallyoutwardly acting force generated by the pressurized working fluid inchamber 42 acting radially outwardly against the inner surface ofcylinder 16. Thus, the inner cylinder 16 is relieved of substantiallyall hoop stresses. either tensile or compressive.

The desired force relationship during the advance stroke of main piston54 may be expressed by the equation:

where K is a constant which reflects the desired differential betweenthe pressures of the support and working fluids and the differentialbetween the transverse cross-sectional areas of main piston 54 andpiston rod 147 which are directly exposed to the working fluid andsupport fluid respectively.

Force 1",, acting through main piston 54 theoretically generates a forceF against the working fluid which is equal in magnitude to F Similarly.the force F. acting through support piston rod 147 generates a force F,against the support fluid which is substantially equal to force F, Thus,the desired force relationship as expressed by equation l for theadvance stroke of main piston 54 also may be rewritten as follows:

Upon the completion of the advance stroke, main piston 54 is retractedby introducing retraction fluid through line 93 to retraction fluidchamber 82 while relieving the pressure on the fluid in advance fluidchamber 81. Concurrently with the introduction of retraction fluid tochamber 82 in main fluid motor 70, retraction fluid is also introducedto retraction fluid section 152 of support fluid motor 129 so as torelieve the pressure of the support fluid in support fluid chamber 44since, during the retraction of main piston 54, there is no fluidpressure load in working chamber 42. Also during the retraction of mainpiston 54, a new charge of working fluid is introduced to chamber 42through bore 95 in piston 54 (FIG. 1 and also shown schematically in H0,2) and check valve 96.

Considering now, with reference to FIG. 2, the specific nature of theproblem caused by piston seal friction which attends the operation ofthe pressure intensifier of P10. 1, it can be seen that during theadvancement of piston 54, the load to be overcome by the advance fluidacting against actuator piston 79, viz. F,,,. is not equal to theworking fluid force F,,., and the force required to overcome frictionalforce F, caused by the surface-to-surface engagement of piston 54 withseal 60. Thus, the force of the advance fluid F on main piston 54 isgreater than the force F of the working fluid on main piston 54 by anamount equal to the frictional force F Conversely, at the completion ofthe advance stroke of main piston 54 and at the commencement of theretraction of main piston 54, the pressure of the working fluid is stillhigh and tends to expel main piston 54 from chamber 42. Thus, at thisstage of the cycle, the force F 1 generated by the pressure of theworking fluid against piston 54 is supported by the actuator fluid inchamber 81 bearing against piston 79, i.e. force F In this case,however, the friction between piston 54 and seal 60 generates a force F,which tends to hold the piston 54 within chamber 42, or in other words,to assist the actuator fluid force F, in supporting piston 54 againstexpulsion, thus rendering the actually required force F less than F, byan amount equal to the force F During the advance stroke of piston 54,therefore, the actuator fluid force can be expressed as follows:

wherein F is the upwardly directed force generated by the working fluidin chamber 42 bearing against the lower surface of main piston 54, and Fis the frictional force between seal 60 and piston 54 tending to resistthe advance of piston 54 into chamber 42.

At the completion of the advance stroke 54 and at the commencement ofretraction, i.e. where downward movement of piston 54 has stopped andthe pressure in working fluid chamber 42 is still high, the actuatorfluid force can be expressed as follows:

wherein F M is again the upwardly directed force generated by theworking fluid in chamber 42 which is tending to expel piston 54 fromchamber 42, and F, is the frictional force between seal 60 and piston 54tending to resist the expulsion of piston 54 from chamber 42. Thus,during advance of piston 54, it can be seen that the force F does notaccurately reflect and, in fact is greater than the force generated bythe working fluid F,,., by a factor equal to the frictional force F,.Similarly, at the completion of the advance of piston 54, force F, isless than the force F M generated by working fluid by an amount equal tothe piston-seal friction force F Relating the effect of the piston-sealfriction force F during an intensification cycle as discussed above, tothe pressure of the fluid in support fluid chamber 44, it was notedabove that proper support for the inner cylinder 16 occurs when equation(2) is satisfied, i.e. when:

it was also noted above that the same actuator fluid which exertspressures on piston 79 in chamber 81 also exerts pressure on piston 148in chamber 151. Thus, any change in the force exerted on piston 79, F isreflected by a proportionate change in the force F. exerted on piston148. Or, as was stated above,

In that pressure amplifier 64 pressurizes rather than displaces fluid,the frictional forces within pressure amplifier 64 can be considered tobe negligible. Thus, it may be said that, in the absence ofcompensation, the force F generated by the actuator fluid against piston148 is always equal to the force F generated by the support fluidagainst piston rod 147. Thus, it may also be said that:

xF lil Substituting equation (5) into equation (2) it may be said thatthe desired support for inner cylinder 16 occurs when:

and since KF. is equal to F, it again becomes clear that the desiredsupport for inner cylinder 16 occurs when the force generated by theworking fluid F is equal to the force against piston 79, F,,. As is seenfrom equations (3) and (4), however, such is not the case when piston 54is moving or tending to move with respect to seal 60. More specifically,when F,,. is greater than F i.e. during piston advance, equation (3)above; F is greater than that force actually required to generate thedesired pressure in the support fluid in chamber 44 and thus the actualpressure generated is in excess of that desired to support innercylinder 16. As noted above, such an excess causes undesirabledeformation of the inner cylinder 16 and may even cause failure of theinner cylinder by implosion.

Conversely, after the advance stroke and upon retraction of piston 54,the force F is less than that exerted by the working fluid F by anamount equal to the piston'seal friction force F equation (4). Thus, insuch a situation, KF is less than the force actually required togenerate the desired pressure in the support fluid in chamber 44 andthus, the actual support pressure generated is less than that desired tosupport inner cylinder 16. As noted above, such a reduction in supportfluid pressure causes undesirable deformation of the inner cylinder 16and may even cause failure of the inner cylinder by explo- SlOn.

The present invention overcomes the deformation and failure tendency ofinner cylinder 16 as discussed above, by the provision of piston-sealcompensator apparatus, including fluid motor 128 of FIG. 2, for sensingthe amount of friction force F, generated by the seal-piston frictionand for transmitting the sensed friction force to exert a controlling orcor rective force on a compensating fluid motor, e.g. the fluid motor130 of FIG. 2, for generating a force component in the support fluidsystem (as shown), or to a fluid motor operatively connected to the mainfluid motor for generating a force component in the working fluid system(not shown), which force component in either situation is equal inmagnitude and opposite in direction to the effect of the seal-pistonfrictional force component. The apparatus for sensing the amount offriction load generated comprises a means for sensing the tendency ofthe pressure vessel to be displaced by the frictional forces.

Referring again to FIG. 1, therefore, it can be seen that pressurevessel is slidably mounted on discharge pipe 56 and slidably receivedwithin stationary mounting cylinder 99. Thus, as piston 54 is advancedinto chamber 42 so as to pressurize and discharge working fluid throughdischarge pipe 56, frictional force F,( FIG. 2) is generated betweenpiston 54 and seal 60 which tends to displace the pressure vessel 10downwardly over discharge pipe 56 arid then within the stationarymounting cylinder 99. Since mounting cylinder 99 is fixed, the .tendencyof pressure vessel 10 to move downwardly within mounting cylinder 99also tends to exert a pressure in the fluid in second annular fluidchamber 112 which comprises one chamber of sensing fluid motor 128. Thepressure exerted on the fluid in chamber 112 is transmitted throughpassage 125, fluid ,line 126 and passage 164 to the retarding fluidsection 157 .of compensator fluid motor 130, and exerts an upwardlydirected retarding force F, (FIG. 2) against compensator piston 149.Force F, is of a magnitude which is equal or substantially equal to thatportion of the force acting on piston 148 which is generated by thepiston-seal friction, viz. F ,/K It can be seen, therefore, that at thisstage of the operation, i.e. during the advancement of piston 54,advance fluid in the advance fluid section 151 of support fluid motor129 is exerting a force F (FIG. 2) on piston 148, which is tending todisplace support fluid piston 148 and therewith piston rod 147downwardly, whereas the fluid in the retarding fluid section 157 ofcompensator fluid motor is exerting a force F, (FIG. 2) which is tendingto displace compensator piston 149 and therewith piston rod 147upwardly. The net effect of the opposed forces acting on piston rod 147,i.e. the downwardly directed force F generated by' the advance fluidwhich reflects both the force F M generated by the working fluidpressure and the seal-piston friction force F and the upwardly directedforce F, generated by the fluid in retarding fluid section 157, whichreflects the seal-piston friction load, is that the forces generated inresponse to seal-piston friction are effectively cancelled, and thesupport fluid in support fluid chamber 44 is pressurized by a force P};which is related solely to the magnitude of the pressure of the workingfluid in chamber 42. The foregoing analysis of the opposed forces actingon piston 147 may also be stated:

sF sf' r which, since F ,=F81/ K by equation l may be written Sf 8 'rSince, from equation (3) F is equal to F -i-F then equation (8) may berewritten:

and since F is equal to KF,, equation (9) becomes:

xf u'f which as was discussed above, corresponds to the desired forcebalance situation for having support fluid in chamber 44 properly assistinner cylinder 16 in supporting the load generated by the working fluidin chamber 42.

Thus, by compensating for the seal-piston friction load by a force whichis equal and opposite to the effect thereof, the

pressure in support fluid chamber 44 is maintained in the desiredrelationship to the pressure in working fluid chamber 42 notwithstandingthe occurrence of piston-seal friction and the above-describeddisadvantageous deformation and failure of the inner cylinder 16 isobviated.

Upon the completion of the advance of piston 54, the introduction ofadvance fluid to advance fluid chamber 81 is stopped, the pressure inchamber 42 is reduced and valve 97 in discharge line 56 closes so as toisolate the intensifier for recharging. in this situation, the workingfluid is tending to expel piston 54 from chamber 42 and as such istending to exert a pressure on the advance fluid in advance fluidchamber 81 through piston 79. The magnitude of the force F transmittedthrough piston 54 to piston 79 for exerting a pressure on the advancefluid in chamber 81 is less than that F exerted on piston 54 by theworking fluid by an amount equal to the seal-piston friction F betweenpiston 54 and seal 60, equation (4). Thus, since the advance fluids inchamber 81 and in advance fluid section 151 are in communication, andsince the establishment of proper pressure in the support fluid inchamber 44 requires that the forces acting on piston rod 147 forpressurizing the support fluid be related to the pressure of the fluidin working chamber 42, the downwardly directed force F exerted by theadvance fluid in advance fluid section 151 of support fluid motor 129,in the absence of compensation, is less than that required to pressurizethe support fluid in chamber 44 sufficiently to support inner cylinder16 without deformation or failure.

As was noted above with respect to the description of the advance ofpiston 54, however, the friction between seal 60 and piston 54 tends tomove pressure vessel 10 within mountchamber 110 is transmitted thro ughpassage 122, fluid line 123 and passage 163 into the booster fluidsection 156 of compensator motor 130 so as to generate a downwardlydirected force F,, against compensator piston 149. Thus, at the end ofan advance stroke by piston 54, and upon the commencement of aretraction stroke, the forces being exerted by fluid pressures withinfluid pressure amplifier 64 include downwardly directed force F by-theadvance fluid in section 151 against support fluid piston 148, anddownwardly directed force F against compensator piston 149 by the fluidin booster fluid section 156. Since the force exerted by the advancefluid reflects the force F, exerted by the pressure of the working fluidin chamber 42 minus the seal-piston frictional force F,, and the forceF,. exerted by the pressure of the fluid in booster fluid section 156also reflects the seal-piston frictional force as sensed by sensingfluid motor 128 and, since both the force F on compensator piston 149and the force F on support fluid piston 148 are directed downwardly, theforces are additive and the net effect of the combined forces on pistonrod 147 is a force which is sufficient to pressurize the fluid insupport chamber 44 by an amount which is the desired relationship to theworking fluid pressure. Thus, the undesirable tendency of inner cylinder16 to deform or fail by explosion under these circumstances iseliminated.

The retraction of piston 54 is efi'ected by relieving the pressure inthe advance fluid system and introducing fluid to the retraction fluidchamber 82 in main fluid motor 70 through fluid line 92 and passage 92.Concurrently, retraction fluid pressure is introduced to the retractionfluid section 152 of support fluid motor 129 from fluid line 93 throughpassage 166. The exertion of retraction fluid in this manner can be seento cause the retraction of piston therewith the introduction of a newcharge of working fluid thereto, as well as the exertion of anunopposed, upwardly directed force on support fluid piston 148 andtherewith piston rod 147 so as to relieve the support fluid pressure inchamber 44. This situation is maintained until piston 54 is fullyretracted at which time the retraction fluid pressure is relieved andadvance fluid pressure is again exerted to commence a repetition of theabovedescribed cycle.

It is to be noted that the above discussion of the operation of theapparatus of FIG. I has been in terms of introducing a compensatingforce which is equal and opposite to the force generated by piston-sealfriction. It should be recognized, however, that the compensating forceneed not always be equal to the frictional force so long as it is ofsufficient magnitude to prevent undesirable deflection and failure ofinner cylinder 16.

The foregoing description directed to the apparatus of FIG. 1, disclosesone embodiment of a seal-friction compensator according to the teachingof the invention wherein the tendency to movement of pressure vessel issensed by a sensing fluid motor 128 which generates a fluid-pressuresignal for transmission to a compensator fluid motor 130 whichintroduces a corrective force directly on a support fluid motor 129which generates pressure in a support fluid system. It is to berecognized, however, that other embodiments of seal-friction compensatorapparatus can be structured in accordance with the present teaching. Forexample, the apparatus shown schematically in FIG. 3 embodies aseal-friction compensator according to the present teaching wherein thetendency of the pressure vessel to be displaced is measured by a loadcell, rather than by a sensing fluid motor as shown in FIG. 1.

More specifically, and referring to FIG. 3, a pressure vessel designatedgenerally by the reference numeral 210 is shown schematically tocomprise an outer cylinder 214, an inner cylinder 216, a top end plug218 and a bottom end plug 219. Inner cylinder 216, top end plug 218 andbottom end plug 219 cooperate to define a working fluid chamber 242.Similarly, inner and outer cylinders 216, 214, top end plug 218 andbottom end plug 219, cooperate to define a support fluid chamber 244.Extending into working fluid chamber 242 through top end plug 218 is amain piston 254 which is driven reciprocably by a main fluid motor 270.The penetration of main piston 254 through top end plug 218 is sealedagainst fluid leakage by a high-pressure seal 260.

Similarly to the embodiment of FIGS. 1 and 2, slidably extending intoworking fluid chamber 242 through bottom end plug 219 is a dischargepipe 256 which is equal in diameter to the diameter of main piston 254.

Working fluid to be pressurized and pumped is introduced through top endplug 218 from a source line 295 having a check valve 296 mountedtherein. Support fluid in chamber 244 is pressurized by a support fluidmotor 229 which is in communication with chamber 244 through a fluidline 226. As was the case with the apparatus of FIG. I, a seal frictioncompensator fluid motor 230 is driven by fluid pressure signals whichare related to the forces generated by the friction between main piston254 and the high pressure seal 260 through which it extends.

The magnitude of the seal friction force generated during the operationof the apparatus of FIG. 3, however, is sensed electrically rather thanhydraulically as was the case with respect to the embodiment of FIG. 1.Specifically, pressure vessel 210 is mounted on a load cell 250 which ismounted on a rigid foundation 252. Output signals generated by load cell240 are transmitted over lead 257 to a servovalve 255 which, in responseto the load cell signals, transmits hydraulic pressure signals tocompensator fluid motor 230.

The operation of the apparatus of FIG. 3 is exactly the same as thatdescribed above with respect to the apparatus of FIG. 1 except for themanner in which seal-friction forces are sensed. Thus, with fluid in allsystems, advance fluid is introduced to main fluid motor 270 and supportfluid motor 229 through advance fluid line 290. The introduction ofadvance fluid to main fluid motor 270 displaces main piston 254downwardly to pressurize and thereafter pump working fluid from chamber242 through discharge line 256. Additionally, the pressure in theadvance fluid exerts a downwardly directed force on the piston ofsupport fluid motor 229 which causes the pressure in the fluid inchamber 244 to be increased so as to assist inner cylinder 216 insupporting the pressure of the fluid in chamber 242. The advance of mainpiston 254 through the high-pressure seal 260 tends to displace pressurevessel 210 downwardly against load cell 250 thereby generating anelectrical signal which is transmitted to servovalve 255 over lead 257.Servo valve 255, in response to the signal from load cell 250, transmitsa hydraulic pressure signal to compensator fluid motor 230 through fluidline 258, which pressure signal exerts an upwardly directed force on thepiston of compensator fluid motor 230. Since the pressure of the advancefluid in support fluid motor 229 generates a downwardly directed forceon the fluid motor piston which reflects both the pressure in workingfluid chamber 242 and the seal-friction force generated between plunger254 and the high-pressure seal 260, and, since the pressure signal fromservovalve 255 to compensator fluid motor 230 causes the generation ofan upwardly directed force against the piston of compensator fluid motor230 which reflects only the seal-friction force, the net effect on theoutput of fluid pressure amplifier 264 is that the upwardly anddownwardly directed forces which result from the piston-seal friction,being equal in magnitude and opposite in direction, are eliminated andthe output of the amplifier, i.e. the pressure exerted on the supportfluid in chamber 244, is properly related to only the working fluidpressure. As such, inner cylinder 216 is properly supported at all timesagainst undesirable deformation and catastrophic failure.

The hydraulic systems shown in FIGS. 1 and 3 are each systems whereinthe utility of the pressure vessel, viz a fluidpressure intensifier, issuch that the operation of the apparatus includes frequent pressurechanges in the working fluid chamber. Specifically, with each advanceand retraction of the main piston, the fluid pressure in the workingchamber is increased to a desired operational level, maintained at thatoperational level during pumping, relieved to recharge the chamber, andthereafter increased once again.

It is to be recognized, however, that the present invention is equallyapplicable to use of the pressure vessel in situations where thepressure of fluid in the working chamber must be maintained constantnotwithstanding relative movement between the main piston and thepressure vessel. Typical of these situations is that where the apparatusis to be used to of the present invention is utilized to introduceforces into the hydraulic system-which are-equal to and vectoriallyopposite the forces generated by seal-piston friction so as to enablethe pressure of the support fluid in the support fluid chamber to bemaintained at a magnitude which is proper for assisting the innercylinder in supporting the fluid pressure load within the working fluidchamber.

it is also to be recognized that the compensator fluid motor utilized inthe present invention can be positioned so as to exert compensatingforces directly upon the main fluid motor rather than on the supportfluid motor as is shown in FIGS. 1 and 3. This can be accomplishedreadily by one skilled in the art, for example by mounting thecompensator fluid motor in tandem with the main fluid motor rather thanin the same manner as is described above. Thus, it can be seen that bymounting the compensator fluid motor in tandem with the main fluidmotor, the friction compensator of the present invention can be used notonly to regulate support fluid pressure, but also to insure a desiredrelationship between working fluid pressure and actuating fluid pressurein situations wherein the pressure vessel being utilized is one whichdoes not provide for support fluid.

it is considered to be manifest that many other modifications andchanges can be made to the disclosed embodiments without departing fromthe spirit and scope of the present invention.

lclaim:

1. in an apparatus for pressurizing fluid including: a working chamberfor containing working fluid, a support chamber surrounding said workingchamber for receiving support fluid, means for pressurizing said workingfluid, and means for pressurizing said support fluid, said working fluidand said support fluid having a predetermined pressure-levelrelationship. the

improvement comprising:

sensing means for sensing any variation in said predetermined pressurelevel relationship; and

compensating means responsive to said sensing means for exertingcompensating controlon said means for pressurizing said support fluid torestore said predetermined pressure level relationship upon thealteration thereof.

2. The improvement accordingto claim 1 wherein said sensing meanscomprises a fluid motor.

3. The improvement according to claim 1 wherein said sensing meanscomprises a load cell.

4. ln fluid pressurization apparatus including: a pressure vesselcomprising a working fluid chamber for containing working fluid, and asupport fluid chamber surrounding said working fluid chamber forcontaining support fluid; a fluid motor including,a piston extendinginto said working fluid chamber for pressurizing said working fluid; asupport fluid motor for pressurizing said support fluid in apredetermined pressure level relationship withrespect to said workingfluid; and sealing means mounted in said pressure vessel and in slidingengagement with said piston for preventing leakage of said working fluidfrom said working fluid chamber, the improvement comprising:

sensing means for sensing frictional forces generated by the slidingengagement of said sealing means with said piston. said frictionalforces tending to alter said predetemiined pressure level relationship;and

a compensator fluid motor responsive to said sensing means for exertingcontrolling force on said support fluid motor to cause said support Uldmotor to vary the pressurization of said fluid to restore saidpredetermined pressure level relationship.

5. The improvement according to claim 4 wherein said sensing meanscomprises a fluid motor.

6. The improvement according to claim 4 wherein said sensing meanscomprises a rigidly mounted cylinder surrounding and loosely receivingsaid pressure vessel and defining in cooperation with said pressurevessel, and associated seals, a plurality of fluid chambers forreceiving fluids which fluids are respectively pressurized by movementof said pressure vessel in response to said frictional forces generatedby said sliding engagement of said sealing means with said piston.

7. The improvement according to claim 4 wherein said sensing meanscomprises a load cell.

L-566-PT UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatenrNo. 3; 57 35 Dated March 23. 1971 JOHN EDWARD BEROSET FRANCIS JOSEPHFUCHS, JR.

lnventor(s) It is certified that error appears in the above-identifiedpatent and that said Lerrers Patent are hereby corrected as shown below:

| Column 2, line 27 (specification page H, line 2 L), delete "when, inactuality, the pressure of the working fluid" Column 3, line 12(specification page 7, line 6) after "outer" insert -cylinder- Column 6,line 22 (specification page 16, line 8), delete "section" (secondoccurrence); line 53 (specification page 17, line 1), after "shown in"insert --FIG. 1 as being integral w the structure of--.

Column 7, line 27 (specification page 19, line "F 1" should have been--F Column 8, line I (specification page 21, lines 9 and 10) after "F'insert but rather it is equal to the sum of f0 F line 25 (specificationpage 22, line I) in Equation 3, change the minus sign to a plus sign;line 38 (specification 1: 22, line in Equation t, change the plus signto a minus s line 68 (specification page 23, line 15) Equation 1,

"KF F F should have been "F KF Column 10, line 18 (specification page27, line 13 afte "piston" insert --rod'--; line 23 (specification page 2line Equation 8, "ICF F should have been --KF F KB Column 11, line 28(specification page 30, line "flui line 92" should have been --fluidline 93--; line 32 (specific page 30, line after "piston" insert --5 Ifrom chamber 42 and--.

Column 12, line 25 (specification page 33, line in), "cel 2 10" shouldhave been -cell 250- Column 1 4, line 31 (amendment claim 15, line 17)after "said" (first occurrence) insert --support- Signed and sealed this19th day of October 1971.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer ActingGozmnissioner of Pat

1. In an apparatus for pressurizing fluid including: a working chamberfor containing working fluid, a support chamber surrounding said workingchamber for receiving support fluid, means for pressurizing said workingfluid, and means for pressurizing said support fluid, said working fluidand said support fluid having a predetermined pressure-levelrelationship, the improvement comprising: sensing means for sensing anyvariation in said predetermined pressure level relationship; andcompensating means responsive to said sensing means for exertingcompensating control on said means for pressurizing said support fluidto restore said predetermined pressure level relationship upon thealteration thereof.
 2. The improvement according to claim 1 wherein saidsensing means comprises a fluid motor.
 3. The improvement according toclaim 1 wherein said sensing means comprises a load cell.
 4. In fluidpressurization apparatus including: a pressure vessel comprising aworking fluid chamber for containing working fluid, and a support fluidchamber surrounding said working fluid chamber for containing supportfluid; a fluid motor including a piston extending into said workingfluid chamber for pressurizing said working fluid; a suppoRt fluid motorfor pressurizing said support fluid in a predetermined pressure levelrelationship with respect to said working fluid; and sealing meansmounted in said pressure vessel and in sliding engagement with saidpiston for preventing leakage of said working fluid from said workingfluid chamber, the improvement comprising: sensing means for sensingfrictional forces generated by the sliding engagement of said sealingmeans with said piston, said frictional forces tending to alter saidpredetermined pressure level relationship; and a compensator fluid motorresponsive to said sensing means for exerting controlling force on saidsupport fluid motor to cause said support fluid motor to vary thepressurization of said fluid to restore said predetermined pressurelevel relationship.
 5. The improvement according to claim 4 wherein saidsensing means comprises a fluid motor.
 6. The improvement according toclaim 4 wherein said sensing means comprises a rigidly mounted cylindersurrounding and loosely receiving said pressure vessel and defining incooperation with said pressure vessel, and associated seals, a pluralityof fluid chambers for receiving fluids which fluids are respectivelypressurized by movement of said pressure vessel in response to saidfrictional forces generated by said sliding engagement of said sealingmeans with said piston.
 7. The improvement according to claim 4 whereinsaid sensing means comprises a load cell.